Method of making a titanium piece having good anti-wear, anti-galling, antiseizure and anti-friction properties



' Jan. 10, 1967 GISSER ETAL 3,297,552

METHOD OF MAKING A TITANIUM PIECE HAVING GOOD ANTI-WEAR, ANTI-GALLING,ANTI-SEIZURE AND ANTI-FRICTION PROPERTIES Original Filed Feb. '25, 1963IST NC FROM INVENTOR. HENRY GISSER ARTHUR SHAPIRO United States Patent 4Claims. (Cl. 204-37) The invention described herein may be manufacturedand used by or for the Government for governmental purposes without thepayment to us of any royalty there- This invention is a divisionalapplication of our co- ,pending patent application, Serial No. 260,925,filed February 25, 1963, entitled, Titanium Piece Having Good Anti-Wear,Anti'Galling, Anti-Seizure and Anti-Friction Properties, now abandoned,and relates to anti-wear and anti-friction alloy concentration gradientson titanium surfaces such that titanium pieces may be usedsatisfactorily in diverse machine applications.

It is well known that titanium is a relatively light metal, its specificgravity being only slightly greater than onehalf that of steel. Titaniumpossesses an exceptionally high strength to-weight ratio and goodcorrosion resistant properties which make it especially useful invarious machine elements as in gearing and the like. Its frictionalproperties, wear and galling resistance, however, need considerableimprovement if titanium is to advance its status in diversifiedmachinery equipment.

Toward this end, much research has been directed to the development ofsuitable lubricants for titanium pieces which would aid in lowering itshigh ooefiicient of friction and thus minimize wear of moving parts. Todate, however, no single lubricant has been found which will give goodservice when used with bare titanium metal.

It is therefore, a broad object of this invention to increase theusefulness of titanium metal in various machine elements.

Another object of the invention is to provide means for improving thefriction and wear properties of titanium.

A more specific object of the invention is to improve the friction andwear properties of titanium by diffusing a second metal into thesurfaces of the titanium.

Other and further objects of the invention will be apparent to thoseskilled in the art upon study of this disclosure and of the singledrawing which graphically represents the variations in hardness of thealloy concentration gradients (or modified surfaces) of our newcompositions.

We have discovered that when silver or gold is diffused into a titaniumsurface resulting in an alloy concentration gradient (see the hardnesscurves in the drawings) the surface (when appropriately lubricated)offers admirable anti-friction, anti-wear, anti-seizure and antigallingproperties to the titanium, considerably simplifying the lubricationproblem on the titanium surface.

Further, we have discovered that the titanium surfaces modified by theaforementioned metals as hereinabove described are receptive tolubrication by conventional lubricants and additives (see Tables III,III, IV and VI).

More specifically, when any of the two metals aforementioned areelectroplated on titanium and the resulting piece is heated in anevacuated furnace, the electroplated surface of the titanium is providedwith an alloy con- Patented Jan. 10, 1967 P? CC centration gradienthaving good anti-wear and anti-friction properties to thereby increasethe usefulness of titanium machine elements.

A typically pure metal piece treated in accordance with our inventionhas the following physical properties given below by way ofillustration.

Table I Tensile yield strength, p.s.i 76,700 Ultimate tensile strength,p.s.i 87,200 Tensile elongation in one inch, percent 23.5 Carboncontent, percent 0.08 Nitrogen content, percent 0.02 Hydrogen content,percent 0.005

Grams Potassium cyanide (C.P.) 11 Gold (as potassium gold cyanide) 8.4Distilled water to make 1 liter of solution.

The temperature of the bath was maintained between 60 and C. and acurrent density of about 2 to 3 arn.p./ft. was employed. Using a goldanode, anelectroplate of about 0.001 inch was obtained after about 2hours.

In electroplating silver, the sandblasted titanium piece was immersedfor about 10 seconds in a striking 'bath of:

02. Silver cyanide (tech.) 0.5 Sodium cyanide (tech.) 8.0

Distilled water to make 1 gallon.

The temperature of the striking bath was about 25 C. with a currentdensity of 20 amp/ft The piece was then transferred to a plating bathhaving the composition:

02. Silver cyanide (tech.) 4.0 Potassium cyanide (C.P.) 7.5 Potassiumcarbonate 6.0

Distilled water to make 1 gallon.

The plating bath temperature may conveniently be about 25 C. while thecurrent density approximates 4 am:p./ft. After 1 hour, a plateapproximately 0.0005 inch thick was produced. Silver anodes were used inboth the striking and plating baths.

The titanium pieces, having been plated with silver or gold to thethickness described in Tables 11 and III, were placed in a suitableelectric oven or furnace which was then evacuated to about 10* mm. ofmercury. The furnace temperature was raised from room temperature toabout 860 C. in a period of 2 /2 to 3 hours, maintained at thistemperature for a period of about 7 hours and the furnace allowed tocool gradually while still evacuated. The penetration of the alloyingmetal into the surface of the titanium may be seen from the drawingwhich shows that for each alloy the hardness first increases to amaximum then falls off and thereafter the hardness finally levels offgenerally to that of the titanium 6 metal itself. The depth ofpenetration for any of the metals used maybe seen from the drawing.

To show efiectiveness of the modified titanium surfaces as preparedabove in reducing friction and wear, and in improving the load carryingcapacity (e.g. cutting down seizing and galling) on the titaniumsurface, coefficient of friction tests, wear tests and extreme pressuretests were run and the resulting data are described in the following.

Before running the coefficient of friction, the treated titanium surfacewas ground down to a depth indicated in the tables. (This was done toinsure that the tests were not being run on the unalloyed metal.)Coefiicient of friction was measured at several depths. It will be seenfrom Tables II and III that in every instance the measurement was madeat a depth below the thickness of the original unditfused plating. Thecoefiicient of friction in Tables II and III are those for the slidingof 52100 steel over the treated titanium surface. Coefficients offriction were run on unlubricated surfaces, surfaces lubricated withcetane, and surfaces lubricated with various additives in cetane asshown in Tables II and III. By comparison of the figures obtained withthe treated surfaces with those obtained with the untreated surface oftitanium, it is seen that the coefiicient of friction is greatly reducedin many instances. It was found that when the coefiicient of friction onuntreated titanium was run, there was extensive stick-slip. This was notthe case with many of the treated surfaces. The Tables also shown thatthe treated surfaces has become susceptible to lowering the coefficientof friction by the addition of active additives.

TABLE II.C ()EFFICIENTS OF FRICTION MEASUREMENTS OF MODIFIED TITANIUMSURFACES WITH VARIOUS LUBRICANTS -Smo0th sliding.

ties of the gold and silver treated titanium surfaces as compared withuntreated titanium surfaces.

TABLE IV.FOUR BALL WEAR TEST Failure Time, minutes Alloying Metal Load,

Cetane Diisopropyl 1 Benzyl Phosphite Disulphide None g Gold 50 "i5 "atSilver 40 20 1 2% solution in cetane. 2 Immediate.

TABLE V.SGAR DEPTH lIgSTTHE FOUR BALL WEAR AlloyingMetal Load, Kg. Scardepth, in.

Gold 10 0. 0015*0. 0005 20 0. 0O25:l;0. 0005 Silver 30 0. 002i0. 0005 InTable VI below, excellent anti wear anti-seizure and anti-gallingproperties of our gold modified titanium surface are shown. The datawere obtained on a Falex \Vear Tester.

The tests were conducted using jaw blocks made from FS2320 steel andpins made from 75 A. titanium. The jaw load was increased from zero to250 pounds by engaging the eccentric arm of the rachet wheel. When TABLEIII.COEFFICIENT OF FRICTION MEASUREMENTS OF MODIFIED TITANIUM SURFACESWITH VARIOUS LUB RICANTS Alloying Original Metal Plating Depth, Tncresyl1 Octyl 1 42% Benzyl l I-Iexachloro- Diisopropyl 1 Thickness, in.Phosphate Mercaptan Chlorinated 1 Disulphide Ethane Phosphate in.Parallin None 0.001 0.22 0.20 0.24 0.20 0.25 0.23 Silver 0.0005 0.00050.11 0.20 0.13 0.17 0.25 0.0s 0.0015 0.25 0.21 0.21 0.21 0.19 0.22 Gold.0.001 0.0005 000 0.09 0.00 008 0.09 0.11 0.0015 0.09 0.12 0.21 0.19 0120.09 0.0025 "0.28 -0.29 =0.20 0.21 0.24 0.24

1 2% in cetane. SticksIip. Smooth sliding.

Wear tests were run on the well known Four Ball the jaw load reached 250pounds the eccentric arm was Wear Tester at 600 r.p.m. and 20 to 25 C.The upper disengaged and the load maintained for one minute. and lowerballs were inch diameter commercially pure Using the same procedure, thejaw load was increased in titanium (75 A.). Surfaces were alloyed inaccordance increments of 250 pounds until failure occurred.

with the aforedescribed procedures. Except for titanium which failed ata 2 kilogram load, the tests were run at intervals of 10 kilograms forone hour. If no failure occurred in one hour, the positions of the ballswere changed so that fresh surfaces were exposed and the test continuedat the next higher load. Accordingly, when failure times for any loadare given in Table IV, it means that at a load of 10 kilograms less,there was no failure for a period of one (1) hour.

Table IV shows the excellent wear resistance proper- TABLE VL-FALEX WEARTEST ONMODIFIED TITANIUM SURFACES Cetane Diisopropyl Bennyl Phosphite 2%Disulphide 2% in Cetane in Cetane Pin Wear, Failure, Wear Failure WearFailue lbs. lbs.

Unmodified:

Titanium 0 0 0 0 0 0 Gold"--- 2, 250 3, 000 1, 500 2, 750 2, 000 3, 000

It is apparent therefore that through the practice of our invention theusefulness of titanium has been considerably extended. When lubricatedas aforedescribed, although not limited to the specific lubricantcompositions described herein, the modified titanium surfaces exhibitanti-wear, anti-galling, anti-seizure and anti-friction properties notheretofore realized in the use of titanium.

We claim:

1. A method for producing a machinable titanium piece having on itssurface a thin layer of a noble metal selected from the group consistingof gold and silver and between said layer and titanium base a thickeralloy concentration gradient of titanium and said noble metal, saidgradient having a hardness exceeding the hardness of said titanium baseover a major portion thereof, said method comprising the steps of:

electroplating said piece with said noble metal,

gradually and strongly heating the electroplated piece in vacuo fromroom temperature,

holding the electroplated piece in vacuo in its strongly heated state,and

allowing the piece to cool gradually in vacuo.

2. The method as described in claim 1 wherein said electroplated pieceis gradually and strongly heated in vacuo from room temperature to afinal temperature of about 860 C. over a period of about 2 /2 hours andwherein said heated electroplated piece is held in vacuo at about 860 C.for about 7 hours.

3. A method as described in claim 1 wherein said metal consists of goldand said electroplating step is carried on until about 0.001 inch ofgold electroplate results.

4. A method as described in claim 1 wherein said metal consists ofsilver and said electroplating step is carried on until about 0.0005inch of silver electroplate results.

References Cited by the Examiner UNITED STATES PATENTS 2/1956 Hands204--46 X 7/1962 Finlay 29198 X

1. A METHOD FOR PRODUCING A MACHINABLE TITANIUM PIECE HAVING ON ITSSURFACE A THIN LAYER OF A NOBLE METAL SELECTED FROM THE GROUP CONSISTINGOF GOLD AND SILVER AND BETWEEN SAID LAYER AND TITANIUM BASE A THICKERALLOY CONCENTRATION GRADIENT OF TITANIUM AND SAID NOBLE METAL, SAIDGRADIENT HAVING A HARDNESS EXCEEDING THE HARDNESS OF SAID TITANIUM BASEOVER A MAJOR PORTION THEREOF, SAID METHOD COMPRISING THE STEPS OF:ELECTROPLATING SAID PIECE WITH SAID NOBLE METAL, GRADUALLY AND STRONGLYHEATING THE ELECTROPLATED PIECE IN VACUO FROM ROOM TEMPERATURE, HOLDINGTHE ELECTROPLATED PIECE IN VACUO IN ITS STRONGLY HEATED STATE, ANDALLOWING THE PIECE TO COOL GRADUALLY IN VACUO.